1. Field of the Invention
The invention relates to a vibration exciter for construction machines, particularly for vibration pile drivers.
2. Description of the Related Art
In construction, vibration pile drivers are used to introduce materials to be pile-driven, such as profiles, for example, into the ground, or to draw them from the ground. The ground is excited using vibrations having a frequency above the natural frequency of the ground, and thereby achieves a “pseudo-fluid”state. The goods to be driven in can then be pressed into the construction ground using a static top load. The vibration is generated by means of rotating imbalances that run in opposite directions, in pairs.
The vibration exciters of such vibration pile drivers are vibration exciters that act in linear manner, the centrifugal force of which is generated by means of rotating imbalances. An essential characteristic of these vibration exciters is the static moment. This variable describes the installed imbalance. In vibration exciters configured as adjustable vibrators, the active variable of the imbalance is adjustable. In order to limit the roller bearing stress, adjustment of the static moment takes place by means of adjustment of the active imbalance of each shaft. In general, a center imbalance is rotated relative to two outer imbalances, in order to set the resulting imbalance in this manner. Because the inner imbalances of all the shafts are connected with one another by way of gear wheels, and the outer imbalances of all the shafts are connected with one another by way of gear wheels or by way of the shafts themselves, the relative angles between outer and inner imbalances are the same on all the shafts. A vibration exciter configured in this manner is disclosed, for example, in DE 20 2007 005 283 U1. In this connection, adjustment of the imbalance groups takes place by way of an additional shaft, which is configured as a phase shifter, in the present case in the form of a pivot motor. A particular construction is leader-mounted vibrators, which are usually equipped with three or four imbalance shafts. Such a leader-mounted vibrator is shown in EP 2 392 413 A2, for example.
The aforementioned vibration exciters fulfill the task set for them. It is desirable, however, to reduce the required adjustment pressure, to be able to do without slipping seals, and to improve the reaction time of the pivot motor provided for changing the static moment.